1. Technical Field of the Invention
The invention concerns a process and a device for the grinding or hobbing of the teeth of face-gears.
2. Prior Art
Thanks to the modern NC technology on present day machine tools, it has become possible to machine the teeth of crown-gears or face-gears to maximum precision by the continuous generating process. The decisive step to this end was the solving of the task of making the required geometrically very intricate worm-shaped tool to the necessary degree of accuracy.
High precision face-gears afford advantages in helicopter gears, amongst other things, because angular drive designs are then possible which would be impossible or at least far more difficult to construct with bevel gears. There are gear designs in existence, for example, which in spite of high transmitted power are of compact dimensions and light in weight, thanks to torque splitting. Torque splitting means that in the course of transmission to an output shaft the input torque is divided up and applied to the same driven gear via two or more tooth engagements. For a specified power, this measure allows the driven gear to be made smaller, and hence lighter.
An advantageous design for such a gear stage with torque splitting requires a driven face-gear which has two opposite sets of teeth on its periphery. Engaging with each of these sets of teeth is a pinion which transmits half of the total torque. It is of particular importance for the optimum exploitation of torque splitting that the division of the torque is very exact. With respect to their angular position about the axis of rotation, therefore, the two sets of face-gear teeth must be aligned very accurately one to the other.
The manufacture of such double-sided face-gears has as yet been very complicated, and must be performed in two operations:
1. Machining of the first set of teeth; then removal, reversal and renewed setting up of the workpiece.
2. Exact alignment of the already machined set of teeth relative to the machining tool, such that the second set of teeth is machined at the specified position relative to the first set; then machining of the second set of teeth.
This process is time consuming, and embodies the risk of accuracy loss.
It is an object of the invention to introduce a process and a device which considerably facilitate the manufacture of such double-sided face-gears, and which assure a higher attainable accuracy. This task is achieved by way of a process for the continuous grinding or hobbing of the teeth of a double-sided face-gear having a first and a second set of teeth on a numerically controlled face-gear grinding or hobbing machine, the machine comprising NC machine axes X, Y and Z and a grinding or hobbing tool, the process comprising the steps of
machining said first set of teeth (3), wherein said face-gear and said grinding or hobbing tool are rotated in a synchronized manner relative to each other during the machining,
moving and aligning said grinding or hobbing tool by means of said NC machine axes X, Y and Z with respect to its angular position and its location relative to said double-sided face-gear in a position required for machining said second set of teeth, wherein said movement and alignment is made without interrupting said synchronization between the rotations of said grinding or hobbing tool and said face-gear, and
machining said second set of teeth
This task is furthermore achieved by a device for the continuous generating grinding or hobbing of teeth of a double-sided face-gear having a first and a second set of teeth on a numerically controlled continuous generating gear grinding or hobbing machine, the device comprising
a work spindle defining a workpiece axis,
a work fixture for setting up said face-gear on said work spindle,
a tool head movable relative to said face-gear via NC-axes X, Y and Z of the grinding or hobbing machine, the tool head comprising a tool spindle and
a worm-shaped tool attached to said tool spindle and located in bearings in said tool head, the tool having on its circumference a first and a second zone, wherein the second zone is located opposite the first zone,
wherein the rotations of said face-gear and said worm-shaped tool being synchronized one to the other according to a total number of teeth of said first set of teeth and a total number of thread starts on said worm tool, wherein due to the constructional form of said tool head, both said first zone and said second zone of said tool can alternatively be brought into machining engagement with said first set of teeth and the second set of teeth of said face-gear, without collision between the latter and said tool head.
The invention is explained in the following by the example of grinding the two sets of teeth of a double-sided face-gear on a numerically controlled continuous generating face-gear grinding machine. It is however equally applicable in the same sense to a numerically controlled face-gear hobbing machine.
According to the invention the process consists in the use of an especially designed tool head that allows the worm-shaped tool to be engaged on two opposite sides to machine the two sets of teeth of a double-sided face-gear in one and the same set-up, without disturbing the synchronization maintained between the grinding worm rotation and workpiece rotation while grinding the first set of teeth.
A number of advantages are thereby gained simultaneously:
1. The removal and resetting of the workpiece to grind the second set of teeth are dispensed with, which shortens the overall machining time substantially.
2. The workpiece and work fixture need therefore only be designed for one set-up configuration.
3. The two machined sets of teeth run very exactly concentric and in angular definition to each other, which results in an improved quality in load distribution.
4. The mutual rotational alignment of the sets of teeth can be effected very easily and to high precision via the control system, which likewise contributes to an increase in the overall gearing quality.
A further special advantage of the process according to the invention is that it is possible to grind topologically corrected double-sided face-gears, where the topology is produced by modifications to the tool flank profile, one after the other without having to re-profile or exchange the tool between the two operations. This is due to the fact that during machining, the working and non-working flanks of both sets of teeth make contact with the same portions of the tool, whereas in the conventional method with resetting of the workpiece between the machining of the first and second sets of teeth the allocation of the tool flanks to the workpiece flanks alters.